Police in the German state of Lower Saxony might ask all 16 to 20-year-olds in the Oldenburg area to take a saliva test, the paper reported.
Investigators believe that a group of young people, among them a girl with a ponytail and a boy in a baseball cap and light-colored jacket, were on the bridge around the time the crime occurred.
After police released a sketch of the suspects and German broadcaster ZDF called for witnesses to come forward, the police special task force has received more than 230 new leads in the case.
"A concrete suspect has yet to be found," said police spokesperson Sascha Weiß on Thursday evening.
A 33-year-old mother of two was killed when an unknown person threw a 6-kilogramme wooden block from a motorway bridge on the A29 motorway near Oldenburg. The block crashed through the windshield and hit the woman, who was sitting in the passenger seat. Also traveling in the car were the victim's husband and two children, aged seven and nine. They were not injured.
The perpetrators fled the scene and are wanted for murder.
According to the police, a similar incident occurred along the same stretch of the A29 several years ago when a stone crashed through the window of a moving vehicle. That time, there were no injuries as no one was sitting in the passenger seat.